● To `color{violet}("comprehend plant-water relations")`, an understanding of certain standard terms is necessary.
● `color{brown}("Water potential" (ψ_w))` is a concept fundamental to understanding `color{violet}("water movement.")`
● `color{brown}("Solute potential" (ψ_s))` and `color{brown}("pressure potential" (ψ_p))` are the two main components that determine `color{violet}("water potential.")`
● Water molecules possess `color{brown}("kinetic energy.")`
● In `color{violet}("liquid and gaseous")` form they are in random motion that is both rapid and constant.
● The greater the `color{brown}("concentration")` of water in a system, the greater is its `color{violet}("kinetic energy or ‘water potential’.")`
● Hence, it is obvious that `color{brown}("pure water")` will have the greatest `color{violet}("water potential.")`
● If two systems containing water are in contact, random movement of water molecules will result in net movement of water molecules from the system with higher energy to the one with lower energy.
● Thus water will move from the system containing water at higher water potential to the one having low water potential.
● This process of movement of substances down a gradient of free energy is called `color{brown}("diffusion.")`
● `color{violet}("Water potential")` is denoted by the Greek symbol `color{brown}("Psi" "or" ψ )`and is expressed in pressure units such as `color{brown}("pascals (Pa).")`
● By convention, the water potential of pure water at standard temperatures, which is not under any pressure,
is taken to be `color{brown}("zero.")`
● If some solute is dissolved in `color{violet}("pure water,")` the solution has fewer free water and the concentration of water decreases, reducing its `color{violet}("water potential.")`
● Hence, all solutions have a lower water potential than `color{violet}("pure water;")` the magnitude of this lowering due to dissolution of a solute is called `color{brown}("solute potential")` or `color{brown}(ψ_s. ψ_s)` is always negative.
● The more the`color{brown}(" solute molecules")`, the lower (more negative) is the s .
● For a solution at atmospheric pressure (water potential) `ψ_w` = (solute potential) `ψ_s`.
● If a pressure greater than atmospheric pressure is applied to `color{violet}(" pure water")` or a solution, its `color{violet}("water potential")` increases.
● It is equivalent to `color{violet}("pumping water ")` from one place to another.
● Pressure can build up in a `color{violet}("plant system")` when water enters a plant cell due to `color{violet}("diffusion causing ")` a pressure built up against the cell wall, it makes the cell `color{brown}("turgid ")` this increases the `color{brown}("pressure potential.")`
● Pressure potential is usually positive, though in plants `color{brown}("negative potential or tension")` in the water column
in the `color{violet}("xylem plays")` a major role in water transport up a stem.
● `color{brown}("Pressure potential")` is denoted as `Psi_p.`
● `color{violet}("Water potential of a cell")` is affected by both solute and pressure potential. The relationship between them is as follows:
`Psi_w = Psi_s + Psi_p`
● To `color{violet}("comprehend plant-water relations")`, an understanding of certain standard terms is necessary.
● `color{brown}("Water potential" (ψ_w))` is a concept fundamental to understanding `color{violet}("water movement.")`
● `color{brown}("Solute potential" (ψ_s))` and `color{brown}("pressure potential" (ψ_p))` are the two main components that determine `color{violet}("water potential.")`
● Water molecules possess `color{brown}("kinetic energy.")`
● In `color{violet}("liquid and gaseous")` form they are in random motion that is both rapid and constant.
● The greater the `color{brown}("concentration")` of water in a system, the greater is its `color{violet}("kinetic energy or ‘water potential’.")`
● Hence, it is obvious that `color{brown}("pure water")` will have the greatest `color{violet}("water potential.")`
● If two systems containing water are in contact, random movement of water molecules will result in net movement of water molecules from the system with higher energy to the one with lower energy.
● Thus water will move from the system containing water at higher water potential to the one having low water potential.
● This process of movement of substances down a gradient of free energy is called `color{brown}("diffusion.")`
● `color{violet}("Water potential")` is denoted by the Greek symbol `color{brown}("Psi" "or" ψ )`and is expressed in pressure units such as `color{brown}("pascals (Pa).")`
● By convention, the water potential of pure water at standard temperatures, which is not under any pressure,
is taken to be `color{brown}("zero.")`
● If some solute is dissolved in `color{violet}("pure water,")` the solution has fewer free water and the concentration of water decreases, reducing its `color{violet}("water potential.")`
● Hence, all solutions have a lower water potential than `color{violet}("pure water;")` the magnitude of this lowering due to dissolution of a solute is called `color{brown}("solute potential")` or `color{brown}(ψ_s. ψ_s)` is always negative.
● The more the`color{brown}(" solute molecules")`, the lower (more negative) is the s .
● For a solution at atmospheric pressure (water potential) `ψ_w` = (solute potential) `ψ_s`.
● If a pressure greater than atmospheric pressure is applied to `color{violet}(" pure water")` or a solution, its `color{violet}("water potential")` increases.
● It is equivalent to `color{violet}("pumping water ")` from one place to another.
● Pressure can build up in a `color{violet}("plant system")` when water enters a plant cell due to `color{violet}("diffusion causing ")` a pressure built up against the cell wall, it makes the cell `color{brown}("turgid ")` this increases the `color{brown}("pressure potential.")`
● Pressure potential is usually positive, though in plants `color{brown}("negative potential or tension")` in the water column
in the `color{violet}("xylem plays")` a major role in water transport up a stem.
● `color{brown}("Pressure potential")` is denoted as `Psi_p.`
● `color{violet}("Water potential of a cell")` is affected by both solute and pressure potential. The relationship between them is as follows:
`Psi_w = Psi_s + Psi_p`